Although it is widely believed that individual differences among infants are not predictive of cognitive ability later in life, this conclusion is based on studies that used infant tests heavily weighted with sensorimotor items. In the proposed 3-year study, a novel design will be employed to assess the extent to which nonmotoric measures at 5 and 7 months of age can predict adult IQ: Correlating midchild scores (average of twin children) with midparent IQ (parental average) provides an "instant" facsimile of a longitudinal study from infancy to adulthood. The proposed research will include 450 infants (200 pairs of twins and 50 singletons) and their 500 parents. The infant measures to be used include some measures that have been suggested as precursors of later IQ: orienting responses; Fagan's measure of preference for visual novelty; strength of hand preference; and verbal and test-taking behaviors. In addition, we shall test the efficacy of infant visual reaction time and a delayed memory version of the Fagan measure in predicting adult IQ. Parents will be tested on a battery of measures that includes the WAIS-R, measures of specific cognitive abilities, and a measure of reaction time as a function of increasing bits of information. In addition to developing a brief, reliable, and easily administered battery of early infancy measures that predicts adult IQ, the proposed research will test two general hypotheses: (1) infant precursors of adult cognitive abilities predict adult general cognitive ability (g, or IQ) rather than specific cognitive abilities; and (2) unlike extant infant tests, infant measures that predict adult IQ show substantial genetic influence, are genetically intercorrelated (as shown by twin cross-correlations), and show genetic continuity from infancy to adulthood (as estimated from our model of midparent/midtwin relationships). The practical significance of this research lies in the diagnostic and therapeutic benefit that will ensue from the ability to predict adult cognitive ability from measures obtained in infancy. Its theoretical significance lies in its re-evaluation of the nature of infant intelligence.